1、BRITISH STANDARD BS 6001-2: 1993 ISO 2859-2: 1985 Sampling procedures for inspection by attributes Part 2: Specification for sampling plans indexed by limiting quality (LQ) for isolated lot inspection UDC 311.213.2:620.113.4:658.562.012.7BS6001-2:1993 This British Standard, having been prepared unde
2、r the directionof the Quality, Management and Statistics Standards Policy Committee, waspublished under the authorityof the Standards Boardand comes into effect on 15January 1993 BSI 02-2000 First published in February 1984 Second edition January 1993 The following BSI references relate to the work
3、on this standard: Committee reference QMS/15 Draft for comment 80/62860 DC ISBN 0 580 21906 2 Committees responsible for this British Standard The preparation of this British Standard was entrusted by the Quality, Management and Statistics Standards Policy Committee (QMS/-) to Technical Committee QM
4、S/15, upon which the following bodies were represented: British Clay plc Clay Pipe Development Association Limited Institute of Metal Finishing Institute of Quality Assurance Ministry of Defence Royal Statistical Society Society of Engineers Incorporated Amendments issued since publication Amd. No.
5、Date CommentsBS6001-2:1993 BSI 02-2000 i Contents Page Committees responsible Inside front cover National foreword ii 0 Introduction 1 1 Scope and field of application 1 2 Definitions 2 3 Choice of sampling plan 2 4 Rules for acceptance and non-acceptance 4 5 Double and multiple sampling plans 4 6 E
6、xamples illustrating how to use this part of ISO 2859 4 7 Compatibility with ISO 2859-1 5 Table A Single sampling plans indexed by limiting quality (LQ) (Procedure A) 6 Table B1 Sampling plans for limiting quality 0,5 % 7 Table B2 Single sampling plans for limiting quality 0,8 % 8 Table B3 Single sa
7、mpling plans for limiting quality 1,25 % 9 Table B4 Single sampling plans for limiting quality 2,00 % 10 Table B5 Single sampling plans for limiting quality 3,15 % 11 Table B6 Single sampling plans for limiting quality 5,0 % 12 Table B7 Single sampling plans for limiting quality 8,0 % 13 Table B8 Si
8、ngle sampling plans for limiting quality 12,5 % 14 Table B9 Single sampling plans for limiting quality 20,0 % 15 Table B10 Single sampling plans for limiting quality 32,0 % 16 Table C Relation between limiting quality (LQ) and consumers risk quality (CRQ) 17 Table D1 Summary of sampling plan propert
9、ies for procedure A 18 Table D2 Selected hypergeometric data for OC curves for zero acceptance plans 19 Table D3 Equivalent sample sizes for single, double and multiple sampling plans 20 Table D4 Equivalent acceptance numbers for single, double and multiple sampling plans 20 Table D5 Correspondence
10、between lot sizes, AQL values in ISO 2859-1 and LQ values (Inspection levels I and II, procedure B) 21 Table D6 Correspondence between lot sizes and sample size code letters (Inspection levels S-1 to S-4 and I to III, procedure B) 21 List of references Inside back coverBS6001-2:1993 ii BSI 02-2000 N
11、ational foreword This Part of BS 6001, having been prepared under the direction of the Quality, Management and Statistics Standards Policy Committee, supersedes BS 6001-2:1984, which is withdrawn. This revision is identical with ISO 2859-2:1985 Sampling procedures for inspection by attributes Part 2
12、: Sampling plans indexed by limiting quality (LQ) for isolated lot inspection, published by the International Organization for Standardization (ISO). It follows the principles and procedures that were given in the 1984 edition of BS 6001-2. In this edition there has been a rearrangement in the seque
13、nce of the tables. The illustrative examples, previously collected in an annex, have been brought into the main body of the text. Other changes are of a minor editorial nature. BS 6001 is published in the following Parts. Part 1: Specification for sampling plans indexed by acceptable quality level (
14、AQL) for lot-by-lot inspection; Part 2: Specification for sampling plans indexed by limiting quality (LQ) for isolated lot inspection; Part 3: Specification for skip-lot procedures. The publication of this revision of Part 2 coincides with the publication of a revision of Part 3. It is envisaged tha
15、t Part 0 will be published identical to ISO2859-0, which is in preparation. Additional information. In addition to the textual errors which have been found in the international text (see below), there are points in the text that will benefit from some commentary. In 0.1, paragraph 2, it is stated th
16、at acceptable quality level (AQL) is defined as a process average. This statement contradicts 5.1 of ISO 2859-1:1989 which asserts (paragraph 3) that the AQL should not be confused with the process average. For guidance see 3.6 of ISO 2859-1 where AQL is defined as the quality level which for the pu
17、rpose of sampling inspection is the limit of a satisfactory process average. Footnote 1 to 1.1 quotes from ISO 2859-1. In line 3 delete “Tables 6 and 7 give process levels” and substitute with “Tables VI and VII give percent nonconforming levels” in order to bring the quote up to date with the curre
18、nt edition of ISO 2859-1. In 3.5.1, paragraph 2, line 5, “LQ 10 ” introduces a notational convention which is not explained in the text. This symbol means the limiting quality level for which there is a 10 % chance of acceptance. The statement in parentheses underneath the title of the OC curve plot
19、s in each of the Table B1 to Table B10 is not complete. Therefore “(Curves are identified by sample size code)” should be deleted and substituted with “(Curves are identified by the sample size code letter and acceptance number)”. For consistency, the limiting quality in the title of Table B4 should
20、 be stated as2,0 % rather than 2,00 %. In Table D1 the purpose of the rectangular box may not be immediately clear. The sentence underneath the box should be deleted and substituted with “Each cell in the table has the above layout and shows the consumers risk (PLQ) and the producers risk point (p,
21、P a ) as indicated”. Cross-references International Standard Corresponding British Standard ISO 2859 BS 6001 Sampling procedures for inspection by attributes ISO 2859-0 a Part 0 Introduction to the BS 6001 attribute sampling system a (Identical) a In preparation.BS6001-2:1993 BSI 02-2000 iii Textual
22、 errors. When adopting the text of the International Standard, the textual errors listed below were discovered. They have been marked in the text and have been reported to ISO in a proposal to amend the text of the International Standard. In 0.1, paragraph 1, first indented line, delete “General int
23、roduction” and substitute “Introduction to the ISO 2859 attribute sampling system”. In 0.1, paragraph 2, line 8, delete “reduction to test and inspection costs” and substitute “reduction in test and inspection costs”. In 1.2, item b), line 2, insert “a” between “one of” and “continuing series”. In 3
24、.3, paragraph 2, line 2, delete “sampling size” and substitute “sample size”. In 3.3, paragraph 3, line 1, delete “these tables” and substitute “this table”. In 3.5.2, lines 14 to 17, delete the sentence “For this reason, inspection level III provided by ISO 2859-1 has not been incorporated in this
25、part of ISO 2859 for limiting qualities greater than 5 %.” In 4.1, line 2, insert “number of” between “specified” and “sample units”. In the title of Table B1 delete “Sampling plans” and substitute “Single sampling plans”. In Table D1, in the rectangle below the title, bottom right, delete “Probabil
26、ity of acceptance at quality (p)” and substitute “Probability of acceptance at quality p (P a )”. In Table D1, the column headed “1,25”, second cell from the bottom, top right entry, delete “0,060” and substitute “0,066”. In Table D1, footnote 1, line 2, insert “point” between “producers risk” and “
27、is”. In Table D1, footnote 2, insert “this” between “of” and “limiting”; after “nonconforming” insert “items”. In Table D2, line 1 of the text following the title, insert “no” between “there are” and “nonconforming” in the second sentence. In Table D2, line 2 of the text following the title, delete
28、“sample (Ac = 0), the” and substitute “sample (Ac = 0). The”. In Table D5, in the column headed “Sample size”, delete “1 500” and substitute“500”. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct a
29、pplication. Compliance with a British Standard does not of itself confer immunity from legal obligations. International Standard Corresponding British Standard ISO 2859-1:1989 Part 1:1991 Specification for sampling plans indexed by acceptable quality level (AQL) for lot-by-lot inspection (Identical)
30、 ISO 2859-3:1991 Part 3:1993 Specification for skip-lot procedures a (Identical) a In preparation. Summary of pages This document comprises a front cover, an inside front cover, pages i to iv, pages1to 22, an inside back cover and a back cover. This standard has been updated (see copyright date) and
31、 may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover.iv blankBS6001-2:1993 BSI 02-2000 1 0 Introduction 0.1 General ISO 2859 comprises four parts: Part 0: General introduction; Part 1: Sampling plans indexed by acceptable quality level (AQL)
32、for lot-by-lot inspection; Part 2: Sampling plans indexed by limiting quality (LQ) for isolated lot inspection; Part 3: Skip lot sampling plan. ISO 2859-1 sampling plans, indexed in terms of AQL, which is defined as a process average, were primarily designed for the assessment of a continuing series
33、 of lots. This enables switching rules to be employed which not only give protection to the consumer (by the switch to tightened inspection and discontinuation where necessary) but also provide an incentive to the producer (by the switch to reduced inspection) with a reduction to test and inspection
34、 costs (when consistently good quality is achieved). However, there is little doubt that in many industrial situations today the switching rules are not applied for a variety of reasons or excuses, not all of which may be valid: a) individual ISO 2859-1 plans are used alone but“AQL” protection is st
35、ill claimed or AQL re-defined, to suit “so-called unique products”; b) “our industry product is special so ISO 2859-1 standard plans need not apply to us”; c) production is intermittent (not continuous); d) production is from several different sources in varying quantities, i.e. “job lots”; e) purch
36、ases are from stock-holders no source data available; f) lots are “small” (use of hypergeometric distribution required); g) lots are “isolated”; h) lots are re-submitted after initial rejection. Consequently, in certain of the above cases consumer protection may need to be attained or measured by ot
37、her methods. This part of ISO 2859 uses the limiting quality to measure consumer protection. It should be remembered, however, that prior information on the suppliers quality assurance system and its effectiveness may play a major part in deciding whether or not to accept a single lot. 0.2 Objective
38、s In an attempt to reconcile the somewhat diverse requests for assistance made over the past few years by committees of international standardizing bodies representing various product sectors, this part of ISO 2859 was drawn up in accordance with the following principles: a) the new LQ plans can be
39、easily integrated with the existing AQL plans in ISO 2859-1; b) the LQ indexing uses a preferred series of values that cannot be confused with the preferred series of AQL values; c) the five basic numbers associated with a single sampling plan, i.e. lot size, sample size, acceptance number, AQL (or
40、quality accepted with probability 0,95) and LQ, appear in the same table, whenever possible. 0.3 Summary The problems associated with acceptance sampling inspection involve defining unambiguously the criteria used to judge discrete individual items supplied in quantity, the quality level expected fr
41、om the manufacturing process, the discrimination offered by the plans and the procedure to be followed when a lot is not accepted. Above all, however, it is necessary to design the sampling scheme so that it may easily be invoked in a purchasing contract. The plans in this part of ISO 2859 make maxi
42、mum use of the established plans given in ISO 2859-1, so that sub-clause 12.6 of ISO 2859-1 (see 1.1) can be made directly operational, by providing a rationalized series of plans indexed in terms of limiting quality(LQ). 1 Scope and field of application 1.1 Scope This part of ISO 2859 establishes L
43、Q sampling plans and procedures for inspection by attributes compatible with ISO 2859-1 that can be used when the switching rules given in ISO 2859-1 are not applied, for example, when lots are of an isolated nature. The plans in this part of ISO 2859 are indexed by a preferred series of limiting qu
44、alities (LQ) with a consumers risk usually below 10 %, but always below 13 %. This method of indexing permits the “ad-hoc” procedure 1)mentioned in sub-clause 12.6 of ISO 2859-1 to be implemented as a standard procedure. 1) ISO 2859-1 sub-clause 12.6.2, states: “If the lot or batch is of an isolated
45、 nature, it may be desirable to limit the selection of sampling plans to those, associated with a designated AQL value, that provide not less than a specified limiting quality protection. Sampling plans for this purpose can be selected by choosing a limiting quality (LQ) and a consumers risk to be a
46、ssociated with it. Tables 6 and 7 give process levels for which the probabilities of lot acceptance under various sampling plans are 10 % and 5 %, respectively.” This part of ISO 2859 establishes preferred values for the LQ and allows the consumers risk to vary as indicated above.BS6001-2:1993 2 BSI
47、 02-2000 NOTEThe plans in ISO 2859-1 are indexed by a preferred series of AQL values and inspection levels. During the inspection of a continuing series of lots the application of switching rules helps to ensure that the process average in that series of lots is kept below the specified AQL. Limitin
48、g quality does not have the same direct relationship with the process average (see 3.5.1). 1.2 Field of application Alternative procedures are provided in this part of ISO 2859 to cater for two situations often met in practice: a) Procedure A, to be used when the supplier and consumer both wish to r
49、egard the lot in isolation. The tables are based on random sampling from finite lots for both consumer and producer risks. This procedure shall be used unless there is a specific instruction to use procedure B. b) Procedure B, to be used when the supplier regards the lot as one of 2)continuing series but the consumer considers the lot received in isolation. The tables are based on random sampling from a finite lot for consumers risk at the limiting quality, but random sampling from a process for the producers risk a
